Triboelectric nanogenerator for harvesting energy from water

ABSTRACT

A generator for harvesting energy from flowing water is disclosed. The generator harvests electrostatic energy as well as mechanical kinetic energy from the flowing water. In one aspect, the generator includes a plurality of blades arranged in a radially outward fashion. Each blade includes an electrode and a surface layer for receiving flowing water carrying triboelectric charges. The flowing water affects a flow of electrons between the electrode and ground. In another aspect, the generator includes a first member with a first electrode, and a second member coupled to the first member about an axis. The second member includes a second electrode, and a surface layer between the first electrode and the second electrode. The second member is rotatable with respect to the axis to change triboelectric charges on the electrodes, and to affect a flow of electrons between the electrodes.

CROSS-REFERENCE

This application claims the benefit of U.S. Provisional Patent Application Ser. No. 62/128,757, filed on Mar. 5, 2015, and U.S. Provisional Patent Application Ser. No. 62/107,855, filed on Jan. 26, 2015, all of which are hereby incorporated by reference to their entireties.

STATEMENT OF GOVERNMENT INTEREST

This invention was made with government support under agreement No. DE-FG02-07ER46394, awarded by the U.S. Department of Energy. The government has certain rights in the invention.

TECHNICAL FIELD DISCLOSED

Embodiments of the disclosed technology generally relate to triboelectric nanogenerators for harvesting energies from water.

BACKGROUND DISCLOSED

There are abundant of water-related energy sources in the environment including, for example, ocean wave, tide, waterfall, and rainwater. Each water source may carry multiple types of energy. For example, a single water drop carries two types of energy, including mechanical kinetic energy and electrostatic energy owing to triboelectric charges caused by its contact with surrounding media.

Since 1867, the Kelvin water dropper has been invented to collect the water electrostatic energy and illustrate the natural generation of electricity in atmospheric phenomena such as thunderstorms. The Kelvin water dropper uses falling water to generate a potential difference by electrostatic induction between two interconnected, oppositely charged systems, and it utilizes the initial instantaneous non-equilibrium status of charge distributions in the liquid rather than the friction between the liquid and air.

Recently, triboelectric nanogenerator (TENG) has been developed to convert mechanical vibration energy into electricity. The working mechanism of TENG is based on a combination of contact electrification and electrostatic induction. Normally, TENG needs a relatively dry condition to provide a stable output, because the surface triboelectrification would be largely reduced or totally eliminated owing to the presence of water.

There is a need for a new prototype TENG to harvest water-related energy. There is also a need to maximize the TENG's output by converting both mechanical kinetic energy and electrostatic energy from water into electricity.

BRIEF SUMMARY DISCLOSED

The disclosed technology relates to energy harvesting. One aspect of the disclosed technology relates to a generator. The generator includes a plurality of blades arranged in a radially outward fashion. Each blade includes an electrode and a surface layer for receiving flowing water carrying triboelectric charges. The flowing water affects a flow of electrons between the electrode and ground.

Another aspect of the disclosed technology relates to a generator having a first component for receiving flowing water carrying triboelectric charges. The first component harvests electrostatic energy from the flowing water. The generator includes a second component coupled to the first component. The second component includes a rotatable disk that rotates when the first component receives the flow water. The second component harvests mechanical kinetic energy from the flowing water during rotation.

Yet another aspect of the disclosed technology relates to a generator for harvesting energy from wind. The generator includes a first member including a first electrode. A second member is coupled to the first member about an axis. The second member includes a second electrode and a surface layer between the first electrode and the second electrode. The second member is rotatable with respect to the axis by wind to change triboelectric charges on the electrodes, and to affect a flow of electrons between the electrodes.

A further aspect of the disclosed technology relates to a self-powered sensor for detecting energy flow rate. The sensor includes a first member including a first electrode. The sensor also includes a second member coupled to the first member about an axis. The second member includes a second electrode and a surface layer between the first electrode and the second electrode. The second member is rotatable with respect to the axis by energy flow to change triboelectric charges on the electrodes, and to affect a flow of electrons between the electrodes. A processor is configured to detect the energy flow rate based on at least one of a measurement of current generated by the flow of electrons and a rotation speed of the second member.

One aspect of the disclosed technology relates to a generator. The generator includes an electrode and a superhydrophobic surface layer for receiving flowing water carrying triboelectric charges. The surface layer includes a TiO2 layer with nanostructures thereon. The flowing water affects a flow of electrons between the electrode and ground.

Another aspect of the disclosed technology relates to a generator. The generator includes a first component for receiving flowing water carrying triboelectric charges, and harvesting electrostatic energy from the flowing water. A second component is coupled to the first component. The second component harvests mechanical kinetic energy from the flowing water. When the first component receives the flowing water, the first component contacts the second component to affect a flow of electrons at the first component and the second component.

A further aspect of the disclosed technology relates to a self-powered sensor for detecting chemical. The sensor includes a triboelectric generator including an electrode and a superhydrophobic surface layer for receiving a solution containing a chemical and water. The chemical removes at least one triboelectric charge from the water. The sensor also includes a power indicator indicative of whether the chemical is present based on power output of the triboelectric generator.

These and other aspects of the disclosed technology are described in the Detailed Description disclosed below and the accompanying figures. Other aspects and features of embodiments of the disclosed technology will become apparent to those of ordinary skill in the art upon reviewing the following description of specific, exemplary embodiments of the disclosed technology in concert with the figures. While features of the disclosed technology may be discussed relative to certain embodiments and figures, all embodiments of the disclosed technology can include one or more of the features discussed herein. While one or more embodiments may be discussed as having certain advantageous features, one or more of such features may also be used with the various embodiments of the disclosed technology discussed herein. In similar fashion, while exemplary embodiments may be discussed below as system or method embodiments, it is to be understood that such exemplary embodiments may be implemented in various devices, systems, and methods of the disclosed technology.

BRIEF DESCRIPTION OF THE DRAWINGS

The following Detailed Description technology is better understood when read in conjunction with the appended drawings. For the purposes of illustration, there is shown in the drawings exemplary embodiments, but the subject matter is not limited to the specific elements and instrumentalities disclosed.

FIG. 1 provides a schematic illustration of a water-TENG according to one aspect of the disclosed technology.

FIG. 2A provides a SEM image of a prepared PTFE thin film with hierarchical micro-/nanostructures according to one aspect of the disclosed technology.

FIG. 2B is a photograph of a large-sized PTFE thin film with a uniform superhydrophobic property according to one aspect of the disclosed technology.

FIG. 3 illustrates a fabrication process of a superhydrophobic PTFE thin film with hierarchical micro-/nanostructures according to one aspect of the disclosed technology.

FIG. 4 provides a SEM image of an AAO template with irregular microstructures and nanometer-sized holes according to one aspect of the disclosed technology.

FIG. 5 schematically illustrates an operating principle of the water-TENG for harvesting energy from a water drop according to one aspect of the disclosed technology.

FIG. 6 schematically illustrates an operating principle of the water-TENG for harvesting energy from flowing water or continuous water drop according to one aspect of the disclosed technology.

FIG. 7A illustates output voltage of the water-TENG according to one aspect of the disclosed technology.

FIG. 7B illustrates output current of the water-TENG according to one aspect of the disclosed technology.

FIG. 7C illustrates a relationship between water drop falling height and inductively transferred charges of the water-TENG according to one aspect of the disclosed technology.

FIG. 7D illustrates dependence of output voltage and output current of the water-TENG on the resistance of the external load according to one aspect of the disclosed technology.

FIG. 7E illustrates dependence of output power of the water-TENG on the resistance of the external load according to one aspect of the disclosed technology.

FIG. 7F illustrates dependence of output energy of the water-TENG on the resistance of the external load according to one aspect of the disclosed technology.

FIG. 8A illustrates output current density of a water-TENG having a hydrophilic Nylon film with a smooth surface according to one aspect of the disclosed technology.

FIG. 8B illustrates output current density of a water-TENG having hydrophobic PTFE film with a smooth surface according to one aspect of the disclosed technology.

FIG. 9A illustates output current density of the water-TENG when harvesting energy from flowing tap water according to one aspect of the disclosed technology.

FIG. 9B illustrates AC output transformed to pulse output in the same direction by a full-wave rectifying bridge according to one aspect of the disclosed technology.

FIG. 9C is a photograph of the water-TENG used as a direct power source to light up 20 LEDs according to one aspect of the disclosed technology.

FIG. 9D illustrates a rectified output of the water-TENG used to charge a commercial capacitor of 33 μF.

FIG. 9E illustrates power density of the water-TENG when harvesting energy from flowing tap water according to one aspect of the disclosed technology.

FIG. 10A provides a schematic illustration of a double-layered water-TENG according to one aspect of the disclosed technology.

FIG. 10B illustrates output current density of the double-layered water-TENG when harvesting energy from flowing tap water according to one aspect of the disclosed technology.

FIG. 11A provides a schematic diagram of an integrated TENG system having a water-TENG and a packaged conventional TENG according to one aspect of the disclosed technology.

FIG. 11B provides a SEM image of a patterned PDMS pyramid array according to one aspect of the disclosed technology.

FIG. 11C illustrates output current density of the water-TENG of the integrated TENG system of FIG. 11A according to one aspect of the disclosed technology.

FIG. 11D provides a photograph of the water-TENG used as a direct power source to light up 20 LEDs according to one aspect of the disclosed technology.

FIG. 11E illustrates output current density of the packaged conventional TENG according to one aspect of the disclosed technology.

FIG. 11F illustrates both the rectified outputs from the water-TENG and the packaged TENG used to charge commercial capacitors of 33 μF according to one aspect of the disclosed technology.

FIG. 11G illustrates output current density of the water-TENG for harvesting energy from spray water drop at a higher water temperature of 65° C. according to one aspect of the disclosed technology.

FIG. 12A provides a structure diagram of a water wheel hybridized triboelectric nanogenerator according to one aspect of the disclosed technology.

FIG. 12B provides a structure diagram of a PTFE thin film with nanostructures according to one aspect of the disclosed technology.

FIG. 12C provides a SEM image of the PTFE thin film with nanostructures according to one aspect of the disclosed technology.

FIG. 12D illustrates a contact angle of the PTFE thin film with nanostructures according to one aspect of the disclosed technology.

FIG. 12E is a photograph of the generator of FIG. 12A according to one aspect of the disclosed technology.

FIGS. 13A-D illustrate the working mechanism of the water-TENG of the generator of FIG. 12A according to one aspect of the disclosed technology.

FIGS. 14A-D illustrate the working mechanism of the disk-TENG of the generator of FIG. 12A according to one aspect of the disclosed technology.

FIG. 15A illustrates V_(oc) curve of the water-TENG of the generator of FIG. 12A according to one aspect of the disclosed technology.

FIG. 15B illustrates V_(oc) curve of the disk-TENG of the generator of FIG. 12A according to one aspect of the disclosed technology.

FIG. 15C illustrates I_(sc) curve of the water-TENG of the generator of FIG. 12A according to one aspect of the disclosed technology.

FIG. 15D illustrates I_(sc) curve of the disk-TENG of the generator of FIG. 12A according to one aspect of the disclosed technology.

FIG. 16A illustrates short-circuit current curve of the water-TENG of the generator of FIG. 12A by using a nylon film according to one aspect of the disclosed technology.

FIG. 16B illustrates short-circuit current curve of the water-TENG of the generator of FIG. 12A by using a smooth PTFE film without nanorods according to one aspect of the disclosed technology.

FIG. 16C illustrates short-circuit current of the disk-TENG of the generator of FIG. 12A with a flowing water rate of 54.4 ml/s, as the superhydrophobic PTFE film of the blades is replaced, according to one aspect of the disclosed technology.

FIG. 17A illustrates dependences of the open-circuit voltage of the water-TENG of the generator of FIG. 12A on the load resistance according to one aspect of the disclosed technology.

FIG. 17B illustrates dependences of the short-circuit current of the water-TENG of the generator of FIG. 12A on the load resistance according to one aspect of the disclosed technology.

FIG. 17C illustrates dependences of the open-circuit voltage of the disk-TENG of the generator of FIG. 12A on the load resistance according to one aspect of the disclosed technology.

FIG. 17D illustrates dependences of the short-circuit current of the disk-TENG of the generator of FIG. 12A on the load resistance according to one aspect of the disclosed technology.

FIG. 18A illustrates dependences of the instantaneously maximum power and power density on the load resistance of the water-TENG of the generator of FIG. 12A according to one aspect of the disclosed technology.

FIG. 18B illustrates dependences of the instantaneously maximum power and power density on the load resistance of the disk-TENG of the generator of FIG. 12A according to one aspect of the disclosed technology.

FIG. 18C illustrates dependences of the V_(oc) and I_(sc) values on the flowing water rate of the water-TENG of the generator of FIG. 12A according to one aspect of the disclosed technology.

FIG. 18D illustrates dependences of the V_(oc) and I_(sc) values on the flowing water rate of the disk-TENG of the generator of FIG. 12A according to one aspect of the disclosed technology.

FIG. 19 illustrates dependence of the rotation speed of the disk-TENG of the generator of FIG. 12A on the flowing water rate according to one aspect of the disclosed technology.

FIG. 20A is a photograph of 20 commercial LED bulbs driven by the generator of FIG. 12A at a flowing water rate of 54 ml/s according to one aspect of the disclosed technology.

FIG. 20B illustrates measured voltage of a 4.7 μF capacitor charged by the generator of FIG. 12A and each component thereof at a flowing water rate of 54 ml/s according to one aspect of the disclosed technology.

FIG. 21A illustrates I_(sc) curve at various wind speeds of the disk-TENG of the generator of FIG. 12A when it is driven by wind according to one aspect of the disclosed technology.

FIG. 21B illustrates dependences of V_(oc) and I_(sc) values on wind speed of the disk-TENG of the generator of FIG. 12A when it is driven by wind according to one aspect of the disclosed technology.

FIG. 22 illustrates dependence of the rotation speed of the disk-TENG of the generator of FIG. 12A on the wind speed according to one aspect of the disclosed technology.

FIG. 23 illustrates short-circuit current curve of the water-TENG of the generator of FIG. 12A without flowing water as it is driven by wind at a wind speed of 15.1 m/s according to one aspect of the disclosed technology.

FIG. 24 provides a schematic illustration of a generator according to one aspect of the disclosed technology.

FIG. 25A provides a SEM image of assembled SiO₂ nanoparticles according to one aspect of the disclosed technology.

FIG. 25B provides a SEM image of a prepared TiO₂ layer with irregular structures according to one aspect of the disclosed technology.

FIG. 26A illustrates a Raman spectrum of the prepared TiO₂ layer according to one aspect of the disclosed technology.

FIG. 26B illustrates an XRD pattern of the prepared TiO₂ layer according to one aspect of the disclosed technology.

FIG. 27A illustrates an advancing contact angle of the prepared TiO₂ layer according to one aspect of the disclosed technology.

FIG. 27B illustrates an advancing contact angle of the prepared TiO₂ layer after coating with PFTS according to one aspect of the disclosed technology.

FIG. 28 illustrates UV-Vis absorption spectra of the MB solution under the solar light irradiation in the presence of the prepared TiO₂ layer according to one aspect of the disclosed technology.

FIG. 29 illustrates a fabrication process of the generator of FIG. 24 according to one aspect of the disclosed technology.

FIG. 30A provides a fluorescence image of E. coli in LB media under the solar light irradiation for 60 min without the prepared TiO₂ layer according to one aspect of the disclosed technology.

FIG. 30B provides a fluorescence image of E. coli in LB media under the solar light irradiation for 60 min with the prepared TiO₂ layer according to one aspect of the disclosed technology.

FIG. 31A illustrates working mechanism of the water-TENG of the generator illustrated in FIG. 24 according to one aspect of the disclosed technology.

FIG. 31B illustrates working mechanism of the contact-TENG of the generator illustrated in FIG. 24 according to one aspect of the disclosed technology.

FIG. 32A illustrates generated V_(oc) from Output 1 of the generator of FIG. 24 under the impact of the flowing water from a household faucet according to one aspect of the disclosed technology.

FIG. 32B illustrates generated V_(oc) from Output 2 of the generator of FIG. 24 under the impact of the flowing water from a household faucet according to one aspect of the disclosed technology.

FIG. 32C illustrates generated I_(sc) from Output 1 of the generator of FIG. 24 under the impact of the flowing water from a household faucet according to one aspect of the disclosed technology.

FIG. 32D illustrates generated I_(sc) from Output 2 of the generator of FIG. 24 under the impact of the flowing water from a household faucet according to one aspect of the disclosed technology.

FIG. 33A illustrates dependence of generated V_(oc) from Output 1 of the generator of FIG. 24 on the resistance of the external load according to one aspect of the disclosed technology.

FIG. 33B illustrates dependence of generated V_(oc) from Output 2 of the generator of FIG. 24 on the resistance of the external load according to one aspect of the disclosed technology.

FIG. 33C illustrates dependence of generated I_(sc) from Output 1 of the generator of FIG. 24 on the resistance of the external load according to one aspect of the disclosed technology.

FIG. 33D illustrates dependence of generated I_(sc) from Output 2 of the generator of FIG. 24 on the resistance of the external load according to one aspect of the disclosed technology.

FIG. 33E illustrates dependence of instantaneous power density from Output 1 of the generator of FIG. 24 on the resistance of the external load according to one aspect of the disclosed technology.

FIG. 33F illustrates dependence of instantaneous power density from Output 2 of the generator of FIG. 24 on the resistance of the external load according to one aspect of the disclosed technology.

FIG. 34 provides a schematic illustration of a generator according to one aspect of the disclosed technology.

FIG. 35A illustrates generated I_(sc) from Output 1 of the generator of FIG. 34 under the impact of the flowing water from a household faucet according to one aspect of the disclosed technology.

FIG. 35B illustrates generated I_(sc) from Output 2 of the generator of FIG. 34 under the impact of the flowing water from a household faucet according to one aspect of the disclosed technology.

FIG. 36 illustrates generated I_(sc) from a single water-TENG under the impact of the flowing water from a household faucet according to one aspect of the disclosed technology

FIG. 37A illustrates a diagram of corresponding circuit connection polarities and a photograph of rectified outputs from Output 1 and Output 2 of the generator of FIG. 34 to drive commercial LEDs according to one aspect of the disclosed technology.

FIG. 37B illustrates charging curves of 33 μF capacitors by the rectified outputs from Output 1 and Output 2 of the generator of FIG. 34 according to one aspect of the disclosed technology.

FIG. 38A illustrates output I_(sc) of the water-TENG generated by deionized water drops according to one aspect of the disclosed technology.

FIG. 38B illustrates output I_(sc) of the water-TENG generated by a solution containing 20% ethanol (percentage by volume) according to one aspect of the disclosed technology.

FIG. 38C illustrates output I_(sc) value of the water-TENG generated by samples containing different concentration of ethanol according to one aspect of the disclosed technology.

FIG. 38D illustrates inductively transferred charges of the water-TENG generated by samples containing different concentration of ethanol according to one aspect of the disclosed technology.

FIG. 39 illustrates a triboelectric series.

DETAILED DESCRIPTION

To facilitate an understanding of the principles and features of the various embodiments of the present invention, various illustrative embodiments are explained below. Although exemplary embodiments of the present invention are explained in detail, it is to be understood that other embodiments are contemplated. Accordingly, it is not intended that the present invention is limited in its scope to the details of construction and arrangement of components set forth in the following description or examples. The present invention is capable of other embodiments and of being practiced or carried out in various ways. Also, in describing the exemplary embodiments, specific terminology will be resorted to for the sake of clarity.

It must also be noted that, as used in the specification and the appended claims, the singular forms “a,” “an” and “the” include plural references unless the context clearly dictates otherwise. For example, reference to a component is intended also to include composition of a plurality of components. References to a composition containing “a” constituent is intended to include other constituents in addition to the one named.

Also, in describing the exemplary embodiments, terminology will be resorted to for the sake of clarity. It is intended that each term contemplates its broadest meaning as understood by those skilled in the art and includes all technical equivalents that operate in a similar manner to accomplish a similar purpose.

Ranges may be expressed herein as from “about” or “approximately” or “substantially” one particular value and/or to “about” or “approximately” or “substantially” another particular value. When such a range is expressed, other exemplary embodiments include from the one particular value and/or to the other particular value.

By “comprising” or “containing” or “including” is meant that at least the named compound, element, particle, or method step is present in the composition or article or method, but does not exclude the presence of other compounds, materials, particles, method steps, even if the other such compounds, material, particles, method steps have the same function as what is named.

It is also to be understood that the mention of one or more method steps does not preclude the presence of additional method steps or intervening method steps between those steps expressly identified. Similarly, it is also to be understood that the mention of one or more components in a composition does not preclude the presence of additional components than those expressly identified. Such other components or steps not described herein can include, but are not limited to, for example, similar components or steps that are developed after development of the disclosed technology.

The materials described as making up the various elements of the present invention are intended to be illustrative and not restrictive. Many suitable materials that would perform the same or a similar function as the materials described herein are intended to be embraced within the scope of the present invention. Such other materials not described herein can include, but are not limited to, for example, materials that are developed after the time of the development of the present invention.

1. Water-TENG 1.1 Structure

FIG. 1 is a schematic illustration of a triboelectric nanogenerator 100 according to one embodiment of the disclosed technology. The triboelectric nanogenerator 100 may also be referred to as water-TENG 100. The water-TENG 100 may harvest energy from flowing water such as household wastewater, spray water drop and ocean wave. For example, the water-TENG 100 may harvest the electrostatic energy from the water drop.

The water-TENG 100 may include a surface layer 102, an electrode 104, and a substrate 108. The surface layer 102 may include a superhydrophobic surface 106. In one embodiment, the surface layer 102 may include a polytetrafluoroethylene (PTFE) thin film. The superhydrophobic surface 106 may include polytetrafluoroethylene (PTFE) hierarchical micro-/nanostructures 110.

FIG. 2A provide a scanning electron microscopy (SEM) image of an exemplary surface layer 102. The inset of FIG. 2A illustrates the SEM image at a higher magnification. The surface layer 102 may be prepared on a large scale. For example, FIG. 2B illustrates a prepared large-sized surface layer with a uniform superhydrophobic property. The large-sized PTFE thin film may have a dimension of 13 cm×33 cm.

As shown in FIG. 2A, the surface 106 of the surface layer 102 may include irregular microstructures, which may be further covered by high-density nanostructures, such as nanorods. In one embodiment, the mean length and diameter of the nanorods may be about 360 nm and 45 nm, respectively. The hierarchical micro-/nanostructures may contain trapped air, which may reduce the actual contact area between the surface layer 102 and a water drop, consequently strengthening the superhydrophobic ability of the surface layer 102.

The superhydrophobic property of the hierarchical micro-/nanostructures-composed thin film 102 may be assessed by measuring the contact angle of a water drop. The inset of FIG. 2B shows the advancing contact angle of the surface layer 102.

In one embodiment, the average value of the measured contact angle of the surface layer 102 is 169°, which exceeds a minimum requirement for a superhydrophobic surface.

The water-TENG 100 may have any effective dimension, including but not limited to, 4 cm×4 cm and 15 cm×15 cm, among many other possibilities.

The surface layer 102 may have triboelectric characteristics, a triboelectric series rating, a triboelectric polarity, or a charge affinity different from that of water. FIG. 39 provides a triboelectric series.

In one example, the surface layer 102 may include a material with a relatively less negative triboelectric series rating. Examples of suitable materials for the surface layer 102 may include, but not limited to, anyone or a combination of the following materials: polyethylene terephthalate (PET), poly (methyl methacrylate) (PMMA), polydimethylsiloxan (PDMS), polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP), poly (vinyl chloride) (PVC), polyimide, metal and alloy, among many other possibilities.

The electrode 104 may include, but not limited to, anyone or a combination of the following materials: metal such as copper, gold, silver and aluminum, indium tin oxide (ITO) and conductive polymer, among many other possibilities.

The substrate 108 may include anyone or a combination of the following materials: PMMA and PET, among other possibilities.

1.2 Fabrication and Assembly 1.2.1 Fabricate Surface Layer

The fabrication process of water-TENG may start from the preparation of the surface layer 102 with superhydrophobic hierarchical structures. FIG. 3 describes a process for fabricating a PTFE thin film which may serve as the surface layer 102.

First, microstructures may be fabricated by blasting an Al foil 302 with sand particles (diameter around 30 μm) using compressed air (4 kgf/cm²). The sand-blasted Al foil 304 may be further anodizing in a 0.3 M oxalic acid solution to obtain an anodic Al oxide (AAO) template 306 with nanometer-sized holes 308. Specifically, the sand-blasted Al foil 304 may be put into the oxalic acid solution and acting as the anode. Another flat Al sheet may be used as the cathode. The distance between those two electrodes may be 5 cm. The operating voltage may be set up at 40 V by using a computer-interfaced power supply. During the anodization process, the solution may be maintained at a temperature of 15° C. by a circulator. As a result, the AAO template 306 with nanometer-sized holes 308 may be obtained. A Hitachi SU8010 field emission scanning electron microscope (SEM) may be used to measure the size and shape of PTFE hierarchical micro-/nanostructures and the pore diameter of AAO template. FIG. 4 provides an exemplary SEM image of the AAO template 306 with irregular microstructures and nanometer-sized holes.

Next, after cleaning the AAO template 306 with water, a commercial PTFE precursor (AF 601S2, 6 wt %, DuPont) may be poured into the AAO template. A conventional vacuum process may be applied to remove the air remaining in the nanoholes.

After the curing at ambient temperature for one day, the solvent may evaporate, leaving behind a PTFE thin film 311 with hierarchical micro-/nanostructures. Finally, the PTFE thin film 311 may be peeled off from the AAO template by using a double-sided tape 312.

1.2.2 Fabricate Electrode on Substrate

In one embodiment, the electrode 104 of the water-TENG may include a Cu thin film. The Cu thin film may have a thickness about 100 nm. In one embodiment, Cu thin films may be deposited on PMMA substrates by a RF magnetron sputtering deposition system. Conducting wires may be connected to the Cu thin films as leads for subsequently electrical measurements.

1.2.3 Assembly

Once the PTFE thin film 311 is peeled off from the AAO template by using the double-sided tape 312, the double-sided tape 312 may then be attached to the Cu electrode 104 deposited poly(methyl methacrylate) (PMMA) substrate to form the complete water-TENG 100.

1.3 Operating Principle

The water-TENG 100 works substantially different from the working mechanism of the Kelvin water dropper. The working mechanism of the water-TENG 100 may include a sequential contact-electrification and electrostatic-induction process.

1.3.1 Single Water Drop

FIG. 5 schematically illustrates the working mechanism of a single-electrode-based water-TENG 100. As shown in step (i), when the water drop 502 falls from the sky or flows through an insulating tube, triboelectricity is created and causes the surface of the water drop 502 to be positively or negatively charged. In one example, each water drop 502 may have a surface charge density of 4.5 μC/m². The charge on the water drop surface may be positive or negative depending on the counterpart that the drop interacts with. For simplicity purposes, positive charges on the water drop surface are used in FIG. 5 to illustrate the process of converting the electrostatic energy to electricity.

With continued reference to FIG. 5, at step (ii), as the positively charged water drop 502 reaches the surface layer 102, a positive electric potential difference may be established between the water drop 502 and ground. In the short-circuit case, the electrons may transfer from ground to the electrode 104 to balance the potential from the water drop 502 and finally reach an equilibrium condition at step (iii). This contributes to an instantaneously positive current. The charge density on the water drop surface and the contact area between the water drop 502 and the surface layer 102 may affect the inductively transferred charges on the electrode 104, which, in turn, may affect the magnitude of the generated current.

At step (iv), once the water drop moves off the surface layer 102, it causes a negative electric potential difference and therefore, the electrons may flow from the electrode 104 to ground, until achieving a new equilibrium at step (i). This process corresponds to another instantaneously negative current. If the water drops and contacts the surface layer 102 periodically, an AC output may be continuously generated. To obtain the maximum electricity output, the water drop should be completely off after contacting the surface layer 102 to keep the surface layer 102 clean for the next cycle. When the surface layer 102 is superhydrophobic, the electricity output may be improved.

1.3.2 Flowing Water and Continuous Water Drop

FIG. 6 illustrates working mechanism of the water-TENG 100 in case of flowing water or continuous water drops such as raindrop. Again, a sequential process of contact electrification and electrostatic induction is involved.

As shown in FIG. 6(b), once water is left on the surface layer 102, a thin water layer 604 may be formed on the surface layer 102 during the energy harvesting process. The water layer 604 may be a positively charged thin layer. As shown in FIG. 6(c), a positive electric potential difference may occur, causing the electrons to transfer from ground to the electrode 104 to balance the potential difference and reach equilibrium. As positively charged water drops 602 fall on the thin water layer 604, another positive electric potential difference may occur between the water drops and ground. Then, electrons may transfer from ground to the electrode 104 to balance the potential difference and achieve equilibrium, as shown in FIG. 6(d). This contributes to an instantaneously positive current.

As shown in FIG. 6(e), once the water drops move off the water thin layer 604, a negative electric potential difference occurs. As a result, the electrons may flow from the electrode 104 to ground, until achieving a new equilibrium as illustrated in FIG. 6(b). This process corresponds to another instantaneously negative current. If the water drops fall on the thin layer-remained water-TENG periodically, continuous outputs may be generated and collected.

1.4 Output Performance 1.4.1 Output Voltage and Output Current

In one experiment, to measure the electrical output of the water-TENG 100, a programmable syringe pump (PHD 2000, Harvard Apparatus) is applied to control the volume and dropping speed of each water drop. In the experiment, the volume of each water drop is fixed at 30 μL, the dropping speed is around 1 m/s when the water drop falls from a height of 90 cm, and the tap water is chosen as the water source. In the experiment, the electrical outputs of water-TENG are measured using a programmable electrometer (Keithley Model 6514) and a low-noise current preamplifier (Stanford Research System Model SR570).

From a 30-μL water drop, the water-TENG 100 may generate a peak voltage of 9.3 V. FIG. 7A illustrates that the output voltage of 9.3 V is switched between zero and a pinnacle value, which correspond to the separated and contacted status.

From a 30-μL water drop, the water-TENG 100 may generate a peak current of 17 μA. FIG. 7B illustrates that the output current reaches a value of 17 μA and exhibits AC behavior, with an equal amount of electrons flowing in opposite directions within one cycle. The inset of FIG. 7B is the magnified output curve in one cycle. The inset of FIG. 7B illustrates that the current peak corresponding to separating has a smaller magnitude but lasts longer than that for contacting. This observation may be explained by the fact that separating corresponds to a slower process and thus a smaller but wider current signal.

1.4.2 Water Falling Distance

The output performance of the water-TENG 100 may depend upon the water falling distance. Specifically, the charge density on the water drop surface may impact the generated output. FIG. 7C illustrates a relationship between the triboelectricity and the water falling distance. The inductively transferred charges on the electrode may be deduced by integrating the current peak of the water-TENG obtained at different falling heights from the contact surface. The inductively transferred charges on the electrode may be proportional to the charge density of water drop. As shown in FIG. 7C, the inductively transferred charges are increased when enlarging the falling height, and finally saturated at a falling height of 20 cm, corresponding to the maximum charges that a water drop can hold. FIG. 7C verifies that the triboelectricity does exist when the water drop falls through the air, and also indicates that the concept may be applied to harvest the raindrop energy from the environment.

1.4.3 Load Resistance

The output performance of the water-TENG 100 may depend upon the load resistance. In one experiment, the electrical output of the water-TENG 100 is measured by connecting the water-TENG 100 directly to loads of various resistances at a falling height of 90 cm. As shown in FIG. 7D, when the resistance is below 0.1 MΩ, the voltage remains close to 0 and the current density almost has no change. When the resistance increases from 0.1 MΩ to 1 GΩ, the voltage through the load generally increases, but the current across the load follows an opposite trend. Therefore, as illustrated in FIG. 7E, the instantaneous power on the load remains small with the resistance below 0.1 MΩ and reaches the maximum value of 145 μW at a resistance of 5 MΩ. The generated output here is from a single water drop. The output energy is also calculated by the time integral of I²R, as illustrated in FIG. 7F. As shown in FIG. 7F, the curve exhibits that the output energy increases as the resistance increases, and gradually saturates at a resistance of 22 MΩ (30 nJ), which is 3 orders of magnitude larger than that of 1 KΩ (0.03 nJ).

1.4.4 Superhydrophobicity

The output performance of the water-TENG 100 may depend upon the superhydrophobic nature of the surface layer 102. In one experiment, the water-TENG 100 is modified by removing the superhydrophobic nature, for example by replacing the superhydrophobic PTFE film 102 with hydrophilic Nylon film and hydrophobic PTFE film with a smooth surface. FIGS. 8A and 8B respectively illustrate the output performance of the two modified water-TENG generators. Both of the results clearly show the importance of superhydrophobic surface.

1.4.5 Output Current Density and Instantaneous Power Density

The water-TENG 100 may be used to collect the energy of a continuously flowing tap water from a kitchen faucet. The output current density and instantaneous power density may reach 15 mA/m² and 0.2 W/m², respectively, when considering the water-TENG dimensions. The output may directly drive 20 light-emitting diodes (LEDs) instantaneously.

In one experiment, the flowing rate of tap water is set up at around 30 mL/s and the distance between the water-TENG and faucet is 20 cm. To highlight the potential application, the generated output is divided by the water-TENG dimensions (4 cm×4 cm). FIG. 9A displays the output current density of the water-TENG. It is noticed that the maximum output current density may reach 15 mA/m² and the signal varies due to the unstable flowing of tap water from the faucet. The output signal becomes zero after the faucet is turned off, revealing that the output is generated from the faucet flowing water. As shown in FIG. 9B, the AC output may be transformed to pulse output in the same direction simply by a full-wave rectifying bridge. The inset of FIG. 9B provides a sketch of exemplary circuit connection polarities. The rectified output may be utilized to drive 20 commercial LEDs instantaneously as illustrated FIG. 9C, and charge a 33-μF capacitor as illustrated in FIG. 9D. The inset of FIG. 9D illustrates a sketch of exemplary circuit connection polarities.

As shown in FIG. 9E, the instantaneous peak to peak power density is determined about 0.2 W/m2 when the water-TENG is connected to a 5 MΩ load resistor.

2. Double-Layered Water-TENG

FIG. 10A illustrates a multilayer-based device 1000 to harvest energy from water according to one aspect of the disclosed technology. The device 1000 may include multiple layers of the water-TENG 100 described earlier. In one example, the device 1000 may be a double-layered water-TENG. The double-layered water-TENG 1000 may be more effective than the single-layered water-TENG 100 in harvesting energy from faucet flowing water. FIG. 10B shows that the double-layered water-TENG 1000 may provide twice generated output as compared to that of single-layered water-TENG as illustrated in FIG. 9A.

3. Hybrid Generator

Flowing water carries two types of energies. One type of energy is electrostatic energy due to the existence of triboelectric charges on its surface as a result of contact with surrounding media due to the contact electrification, such as contact with air/solid surface during its traveling processes in pipe and/or air. The other type of energy is mechanical kinetic energy.

The disclosed technology includes various embodiments of a hybrid triboelectric nanogenerator designed to simultaneously harvest the electrostatic and mechanical kinetic energies of flowing water. Detailed discussions with respect to these alternative embodiments are provided herein.

3.1 Water-TENG and Packaged TENG 3.1.1 Structure

FIG. 11A illustrates an integrated energy collection system 1100 including a water-TENG 100 (also denoted by (i) in the figure) and a packaged TENG 1110 (also denoted by (ii) in the figure) according to one aspect of the disclosed technology. The water-TENG 100 may harvest the electrostatic energy, whereas the packaged TENG 1110 may harvest the mechanical energy. The system 1100 may effectively collect, including but not limited to, the spray water drop energy as well as the raindrop energy, among other possibilities.

3.1.2 Fabrication of Packaged TENG 3.1.2.1 Fabricate PDMS Film

Fabrication of the packaged TENG 1110 may start from the design of PDMS film with patterned pyramid array as illustrated in FIG. 11B. The inset of FIG. 11B is a SEM image at a higher magnification.

At first, a Si wafer may be molded using photolithography. Then, the wafer may be etched through a dry etching process, resulting in the Si wafer mold with a notched pyramid feature. After a clean wash by acetone and ethanol, the prepared Si wafer mold may be treated with chlorotrimethylsilane to avoid the adhesion between PDMS and Si in the next step. A PDMS mixture may be spin-coated (1000 rpm, 1 min) on the Si wafer mold and then incubated at 60° C. The PDMS may include PDMS elastomer and cross-linker in a ratio of 5:1. After 24 hours, a uniform PDMS film with patterned pyramid array may be formed.

3.1.2.2 Fabricate Electrode on Substrate

100 nm of Cu thin films may be deposited on two Kapton substrates (127 μm, DuPont) by a RF magnetron sputtering deposition system. Conducting wires may be connected to the Cu thin films as leads for subsequently electrical measurements.

3.1.2.3 Assembly

The formed PDMS film with patterned pyramid array may be peeled from Si wafer mold and then placed onto a Cu thin film-deposited Kapton substrate with uncured PDMS mixture on the top, then incubating at 60° C. for another 24 hours. Finally, those two Kapton substrates may be assembled by using a 60-μm-thick hot-melt ionomer film (Surlyn 1702, DuPont) under heating at 150° C. for 10 min and a fully packaged TENG is obtained.

3.1.3 Output Performance

In one experiment, to measure the output performance of the system 1100, the water-TENG 100 is configured to dimensions of 15 cm×15 cm. In the experiment, a household shower jet system is used for the demonstration of the spray water drop. FIG. 11C illustrates that the water-TENG 100 of the system 1100 may achieve a maximum output current density of 1.5 mA/m². The water-TENG 100 may be the primary source for harvesting energy from the spray water drop. The rectified output may successfully power 20 commercial LEDs instantaneously as illustrated in FIG. 11D.

Also from FIGS. 11E and 11F, the packaged TENG 1110 may also successfully collect the mechanical energy of spray water drop. The packaged TENG 1110 may act as the secondary source for harvesting energy from the spray water drop.

The rectified outputs of the system 1100 including the water-TENG 100 and the packaged TENG 1110 may charge a 33-μF capacitor as illustrated in FIG. 11F. The generated output of the water-TENG 100 may not be impacted by a higher water temperature of 65° C., as illustrated in FIG. 11G.

3.2 Water-TENG and Disk-Teng 3.2.1 Structure

FIG. 12A illustrates a structure diagram of a water wheel hybridized triboelectric nanogenerator 1200. The generator 1200 may include a first component 1210 for receiving flowing water carrying triboelectric charges and harvesting electrostatic energy from the flowing water. The first component may be referred to as a water-TENG 1210. The generator 1200 may include a second component 1220 coupled to the first component for harvesting mechanical kinetic energy from the flowing water. The second component may be referred to as a disk-TENG 1220.

The water-TENG 1210 my include a plurality of wheel blades 1212. The plurality of blades 1212 may be arranged in a radially outward fashion. The plurality of blades 1212 may exhibit a wheel-like structure 1214. In one example, the water-TENG 1210 may include 8 blades and operate as a single-electrode-based triboelectric nanogenerator to harvest the electrostatic energy from flowing water.

Each blade 1212 may have a surface layer 1306 for receiving flowing water. The surface layer 1306 may be superhydrophobic. The surface layer 1306 may include a plurality of nanosturctures thereon. In one example, the surface layer 1306 may include a material with a relatively less negative triboelectric series rating. Examples of suitable materials for the surface layer 102 may include, but not limited to, anyone or a combination of the following materials: polyethylene terephthalate (PET), poly (methyl methacrylate) (PMMA), polydimethylsiloxan (PDMS), polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP), poly (vinyl chloride) (PVC), polyimide, metal and alloy, among many other possibilities.

Each blade 1212 may include an electrode 1308. An electrical channel may be formed between the electrode on each blade and ground. The electrode 1308 may include, but not limited to, anyone or a combination of the following materials: metal such as copper, gold, silver and aluminum, indium tin oxide (ITO) and conductive polymer, among many other possibilities.

The electrode 1308 may be deposited on a substrate 1310. The substrate 1310 may include anyone or a combination of the following materials: PMMA and PET, among other possibilities.

The flowing water that falls upon each blade 1212 may carry triboelectric charges. The flowing water may affect a flow of electrons between the electrode 1308 and ground. The flowing water impacted on the blades 1212 may induce rotation of the disk-TENG 1220.

The disk-TENG 1220 may have a disk configuration. The disk-TENG 1220 may include two disks, a front disk 1222 and a back disk 1224. Each disk may exhibit a segmented disk profile. For example, each disk may include 16 segments as illustrated in FIG. 12A. Each disk may include an electrode. For example, as illustrated in FIG. 12A, the front disk 1222 may include a front electrode 1402, and the back disk 1224 may include a back electrode 1406. Each electrode may include, but not limited to, anyone or a combination of the following materials: metal such as copper, gold, silver and aluminum, indium tin oxide (ITO) and conductive polymer, among many other possibilities.

The back disk 1224 may include a surface layer 1404 over the electrode 1406. The surface layer 1404 may be superhydrophobic. The surface layer 1404 may include a plurality of nanosturctures thereon. The surface layer 1404 may include anyone or a combination of the following materials: polyethylene terephthalate (PET), poly (methyl methacrylate) (PMMA), polydimethylsiloxan (PDMS), polytetrafluoroethylene (PTFE), fluorinated ethylene propylene (FEP), poly (vinyl chloride) (PVC), polyimide, metal and alloy, among many other possibilities.

A smooth metal rod 1230 may travel through the centers of the wheel-like structure 1214 and the two disks along the rotation axis “A”.

The front disk 1222 may be fixed on the rotation axis and stays motionless during the whole process. A screw behind the back disk 1224 may be used to adjust the distance between the two disks. A closer contact can induce higher effective contact area, tribo-charge density, V_(oc), and I_(sc), while largely increasing the rotation resistance between the two disks. In one embodiment, the two disks may moderately contact in a low rotation resistance status, as seen in FIG. 14A. In FIG. 14A, the surface layer 1404 of the back disk 1224 is positioned between the back electrode 1406 and the front electrode 1402. The disk-TENG 1220 may harvest the mechanical energy of the water, in which an electrical channel is formed between the electrodes of the two disks.

The back disk 1224 may be rotatable with respect to the rotation axis “A” by energy flow, such as flowing water or wind, to change triboelectric charges on the front electrode 1402 and the back electrode 1406. Rotation of the back disk 1224 may affect a flow of electrons between the electrodes 1402 and 1406.

The back disk 1224 may be connected to the wheel-like structure 1214. The back disk 1224 may be rotatable such that it may rotate when the water-TENG 1210 receives the flowing water. For example, when a blade 1212 receives the flowing water, the blade 1212 may gather the flowing water force. The blade 1212 may induce rotation of the water-TENG 1210 and the back disk 1224 about a rotation axis “I” as depicted in FIG. 12A. The blade 1212 may gather the flowing water force to drive the rotation of the wheel-like structure 1214 and the back disk 1224.

The back disk 1224 may rotate together with the blades 1212 under the impact of flowing water. The disk-TENG 1220 may harvest mechanical kinetic energy from the flowing water during rotation.

In one example, each blade 1212 as well as the back disk 1224 may include a superhydrophobic surface layer. The surface layer may include high-density PTFE nanostructures 1240 as illustrated in FIG. 12B. In one embodiment, the surface layer may include a PTFE film. FIG. 12 C provides a SEM image of the surface layer. In one embodiment, the mean length and diameter of the PTFE nanostructures 1240 may be 360 nm and 45 nm. The contact angle of the surface layer may be 162°, as illustrated in FIG. 12D. The high-density nanostructures 1240 covered on the surface layer may contain trapped air and reduce the actual contact area between the surface layer and water droplets, which increases the superhydrophobic ability. The nanostructures 1240 on the surface layer may increase the effective contact area of two tribo-surfaces and enhance the electrical output of the disk-TENG 1220.

FIG. 12E is a photograph of the generator 1200. In one embodiment, the generator 1200 may include a PET sheet between the blades 1212 and the back disk 1224 to prevent the disk-TENG 1220 from water when the generator is at work. However, for the purpose of clearly showing the structure of the generator 1200, the PET sheet is not shown in the structure diagram FIG. 12A nor the photograph FIG. 12E of the generator 1200.

3.2.2 Fabrication

The generator 1200 may be fabricated according to the following exemplary process. To fabricate the blades 1212, a 100-nm thin Cu film may be deposited on a square Polyethylene terephthalate (PET) sheet to serve as the electrode layer. The PET sheet may have a thickness of 0.5 mm. The PET sheet may be processed by laser cutting (e.g., PLS6.75, Universal Laser Systems) to serve as the substrate of the blades. A Cu film, e.g., of thickness of 100 nm, may be deposited on the substrate by e-beam evaporator. A PTFE film with nanostructures fabricated by using porous anodic Al oxide (AAO) as template may be attached onto the Cu electrode by using a double-sided tape. The Cu electrodes of the 8 blades may be electrically connected together.

To fabricate the disks 1222 and 1224, two Poly(methyl methacrylate) (PMMA) sheets may be first processed by laser cutting to form the 16-segment-structured circle disks as the substrates of the disks 1222 and 1224. The PMMA sheets may have a thickness of 3 mm. For the back disk, a 100-nm thin Cu film may be deposited on one PMMA substrate by e-beam evaporator. Then, a PTFE film with nanostructures may be attached onto the Cu electrode by using a double-sided tape. For the front disk, another 100-nm thin Cu film may be deposited on the other PMMA substrate and directly used as the contact material. The PTFE layer of the back disk and the Cu layer of the front disk may be brought to a face-to-face intimate contact to form a sliding TENG operating at a rotation disk mode.

The smooth metal rod 1230 may be used as a rotation axis to assemble the generator 1200 through the centers of the blades 1212 and the two disks 1222 and 1224.

3.2.3 Operating Principle 3.2.3.1 Operating Principle of Water-TENG

FIGS. 13A-D schematically illustrate the working mechanism of the water-TENG 1210 of the generator 1200.

As shown in FIG. 13A, flowing water 1302 may have positive tribo-charges due to the contact electrification between the water and the pipe/air during its traveling processes. As the flowing water reaches the blade-1, a positively charged water film 1304 may be formed on the surface layer 1306 of the blade-1, because of the tribo-charges created between the water and the water pipe. As a result, a positive potential difference may be created between the electrode 1308 of the blade-1 and ground, which may drive the electrons to transfer from ground to the electrode 1308 of the blade-1 and generate a positive current until the potential difference is decreased to zero. Because the flowing water impacted on the blade-1 may also cause the rotation of wheel, the flowing water may next contact the blade-2 as illustrated in FIG. 13C. Then, another positively charged water film 1304 may form on the PTFE surface of the blade-2, consequently, another positive potential difference may be created between the electrode 1308 of the blade-2 and ground, attributing a positive current until the potential difference is decreased to zero. After this, as illustrated in FIG. 13D, the water film with its positive charges may move off the surface layer, e.g., the PTFE film, of blade-1 due to the continuous rotation of blades and the superhydrophobic property of the surface. With continued reference to FIG. 13D, with the removal of the water film from the blade-1, a negative potential difference may be generated between the electrode of blade-1 and ground because of the negative charges on the electrode, which drives the electrons to transfer from the electrode to ground and generates a negative current until the potential difference becomes zero. With the continuous rotation of the blades, the water reaches different blades in sequence. Alternative positive and negative current may be generated with similar processes as shown in FIGS. 13C-D.

The superhydrophobicity of the surface layer on the blades plays a key role for the removal of the water film. As a result, the superhydrophobicity enhances the electrical output of the water-TENG.

3.2.3.2 Operating Principle of Disk-TENG

FIGS. 14A-14D schematically illustrate the working mechanism of the disk-TENG 1220 of the generator 1200. In the initial stage, the front disk 1222 and the back disk 1224 may fully contact each other. As illustrated in FIG. 14A, the positive and negative tribo-charges may be generated on the Cu electrode surface 1402 of the front disk 1222 and the PTFE surface 1404 of the back disk 1224, respectively, since PTFE has stronger tendency to gain electrons than Cu in the triboelectric series. At the initial stage, the positive and negative charges may fully overlap with each other, and thus there is no potential difference between the Cu electrodes of the two disks and no current is generated. With the rotation of the back disk, the two disks are partly separated as shown in FIG. 14B, and a positive potential difference on the front electrode 1402 is formed, which drives the electrons to flow from the back electrode 1406 to the front electrode 1402 and generates a positive current. As the two disks are fully separated as shown in FIG. 14C, the induced positive charges on the back electrode 1406 may reach its maximum value, and the net charges on the front electrode 1402 may decrease to zero. As the back disk 1224 continues rotating, the front electrode 1402 begins to contact the PTFE film 1404 of another adjacent segment of the back disk as shown in FIG. 14D, and then a negative potential difference is formed on the front electrode 1402, which drives the electrons to flow from the front electrode 1402 to the back electrode 1406 and generates a negative current. Next, the two disks fully contact with each other again as shown in FIG. 14A, the induced charges in the back electrodes 1406 fully flow to the front electrode 1402. With the further rotation of the back disk 1224, another cycle similar to the processes from FIG. 14A to 14D will start.

3.2.4 Output Performance 3.2.4.1 Output Voltage and Output Current

In an experiment to measure electrical output properties of the generator 1200, tap water flowing from a household faucet at a flow rate of 54 ml/s is used to drive the generator 1200, and the vertical distance between the water outlet of the faucet and the rotation axis of the generator 1200 is around 25 cm. In the experiment, current meter (SR570 low noise current amplifier, Stanford Research System) and voltage meter (6514 system electrometer, Keithley) are used to measure the electric outputs of the generator 1200.

FIG. 15A and FIG. 15B illustrate curves of open-circuit voltage, V_(oc), of the water-TENG 1210 and the disk-TENG 1220, respectively. Their magnification curves are shown in the insets. As illustrated, at a flowing water rate of 54 ml/s, the open-circuit voltage V_(oc) of the water-TENG 1210 and the disk-TENG 1220 may be about 72 and 102 V, respectively. The positive V_(oc) value of the water-TENG 1210 indicates the positive tribo-charges in the flowing water from the household faucet.

FIGS. 15C-D illustrate curves of the short-circuit current (I_(sc)) of the water-TENG 1210 and the disk-TENG 1220. Their magnification curves are shown in the insets. As illustrated, at a flowing water rate of 54 ml/s, the short-circuit current I_(sc) of the water-TENG 1210 and the disk-TENG 1220 may reach 12.9 and 3.8 μA, respectively.

By integrating the absolute values of the I_(sc) curve of the water-TENG 1210, the collected charge in a unit time is 0.68 μQ/s. Therefore, the carried tribo-charge in the flowing water in a unit time is 0.34 μQ/s, and the corresponding tribo-charge density in the flowing water from faucet is 6.3 nQ/ml. The mean interval time between two positive current peaks of the water-TENG 1210 and the disk-TENG 1220 are around 0.03 and 0.015 s, respectively, and the corresponding output frequencies are 33.3 and 66.7 Hz, respectively. The output frequency of the TENG with multiple segments may be expressed by f=nN/60, where n is the number of the divided segments in the generator 1200 and N is the rotation speed in a unit of rounds per minute (rpm). According to this equation, the rotation speed of the generator 1200 at a flowing water rate of 54 ml/s is around 249 rpm. Since the two components 1210 and 1220 of the generator 1200 have the same rotation speed and the segment number of the disk-TENG 1220 (16) is two times of that of the water-TENG 1210 (8), the output frequency of the disk-TENG 1220 is two times of that of the water-TENG 1210. Increasing the segment number in the disk and the blades number in the blades can increase the output frequency of the disk-TENG 1220 and the water-TENG 1210, respectively.

For the water-TENG 1210, the positive and negative current peaks correspond to the processes of the formation and the removal of the positively charged water film on the blade surface, respectively. As shown in FIG. 15C, the positive current peak of the water-TENG 1210 is remarkably higher than the negative current peak, which indicates that the removal process of the water film requires longer time than the formation process.

3.2.4.2 Superhydrophobicity

In another experiment, the superhydrophobic PTFE film on the blades is replaced by a hydrophilic nylon film and a hydrophobic smooth PTFE film without nanorods to test the effect of the superhydrophobicity on the output performance of the generator 1200. With the use of a nylon film in the blade surface and the same experiment conditions, the periodically sharp current peaks disappear and only some irregular peaks around 0.4 μA are present as shown in FIG. 16A. With the use of a smooth PTFE film of contact angle about 120° and the same experiment conditions, the I_(sc) peaks of the water-TENG 1210, as illustrated in FIG. 16B, decrease about 60% compared to that using superhydrophobicity PTFE film with nanorods. As shown in FIG. 16C, the I_(sc) curve of the disk-TENG 1220 stays almost the same as that using the superhydrophobicity PTFE film with nanorods in the blades. The comparison result indicates that superhydrophobic surface of the blades plays a critical role for the removal of the water film on the blade surface and is helpful for enhancing the output performance of the water-TENG 1210. Since the disk-TENG 1220 is designed to harvest the mechanical energy of the flowing water, its output performance is independent of the hydrophobic property of the blades surface.

3.2.4.3 Load Resistance

In order to investigate the output power of the generator 1200 at an external load resistor, the output voltage and output current of the water-TENG and the disk-TENG at various load resistances ranging from 100Ω to 1 GΩ are measured, and the corresponding output power value at each resistance is calculated by using P=IV. FIGS. 17A-D illustrate dependences of the output voltage and output current of the water-TENG 1210 and the disk-TENG 1220 on the load resistance. FIGS. 18A and 18B show dependences of the instantaneously maximum output power and the corresponding power density (the output power per contact area of the generator) of the water-TENG 1210 and the disk-TENG 1220, respectively. For the water-TENG 1210, the instantaneously maximum power of 0.24 mW appears at a load of 88 MΩ, and the corresponding instantaneously maximum power density is 0.59 W/m². For the disk-TENG 1220, the instantaneously maximum power of 0.17 mW appears at a load of 88 MΩ, and the corresponding instantaneously maximum power density is 0.03 W/m². The V_(oc) and I_(sc) of the water-TENG 1210 and the disk-TENG 1220 at various flowing water rates ranging from 7 to 54 ml/s are measured. The dependences of V_(oc) and I_(sc) on the flowing water rate for the water-TENG 1210 are shown in FIG. 18C, in which V_(oc) values stay almost constant at about 72 V for various flow rates, and the I_(sc) value increases from 4.3 to 12.9 μA as the flowing water rate increases from 7 to 54 ml/s. The increase of the I_(sc) is caused by more tribo-charges carried in the flowing water in a unit time at a higher flowing rate. The dependences of V_(oc) and I_(sc) on the flowing water rate for the disk-TENG 1220 are shown in FIG. 18D, in which V_(oc) values stay almost constant at about 101 V for various flowing rates, and the I_(sc) value increases almost in a linear fashion with respect to the flowing water rate. For the generator 1200 operating at the rotation disk mode, the I_(sc) values may increase linearly with respect to the rotation speed of the disk. As shown in FIG. 19, the rotation speed of the generator 1200 increases linearly with the flowing water rate, which is the reason for the linear increase of the I_(sc) values of the disk-TENG 1220. This linear dependence of the I_(sc) value on the flowing water rate demonstrates its potential application as a self-powered sensor for detecting flowing water rate. In one example, the self-powered sensor may detect energy flow rate, including but not limited flowing water rate and wind speed, among other possibilities. The self-powered sensor may include a processor configured to detect the energy flow rate. In one embodiment, the processor may detect the energy flow rate based on a measurement of current generated by the flow of electrons. In addition or as an alternative, the processor may detect the energy flow rate based on a rotation speed of the back disk 1224.

3.2.5 Application 3.2.5.1 LEDs

For practical applications in driving LEDs or charging a capacitor, the electrical output of the water-TENG 1210 and the disk-TENG 1220 may be connected in parallel after they are converted to pulse output in the same directions by using two full-wave rectifying bridges, as shown in the inset of FIG. 20A. As the generator 1200 is driven by water at a flow rate of 54 ml/s, 20 commercial green LEDs may light up, as shown in FIG. 20A. The generator 1200 may charge a capacitor of 4.7 μF at a flowing water rate of 54 ml/s. FIG. 20B illustrates the voltage curves of the capacitor. When the capacitor is charged by the rectified output of the water-TENG 1210 and the rectified output of the disk-TENG 1220, respectively, it takes about 596 s and 435 s to charge the capacitor to a voltage of 13 V, respectively. When using the generator 1200 as a whole, it takes 326 s to charge the capacitor to a voltage of 13 V.

3.2.5.2 Wind

The generator 1200 may harvest wind energy and act as a self-powered sensor to detect the flowing water rate and wind speed.

Since the rotation of the blades 1212 may be driven by wind, the generator 1200 may harvest the wind energy. The wind with various speeds may drive the rotation of the disk-TENG 1220. The back disk 1224 may rotate with respect to the rotation axis “A” under the influence of the wind. As a result, the triboelectric charges on the front and back electrodes 1402 and 1406 may change during this process, and affect a flow of electrons between the electrodes 1402 and 1406.

FIG. 21A illustrates the measured I_(sc) curve of the disk-TENG 1220. With the increase of the wind speed, the output frequency and I_(sc) value remarkably increase. FIG. 21B illustrates dependences of the V_(oc) and I_(sc) values of the disk-TENG 1220 on the wind speed ranging from 1.7 to 15.1 m/s, in which the V_(oc) value stays almost constant at about 101 V for various wind speeds, and the I_(sc) value increases almost in a linear fashion with respect to the wind speed. As shown in FIG. 22, the rotation speed of the disk-TENG 1220 increases linearly with the wind speed, and this causes the linear increase of the I_(sc) value based on the similar reason discussed in FIG. 18D. The linear dependence of the I_(sc) values on the wind speed demonstrates its potential application as a self-powered sensor for detecting wind speed. When the generator 1200 is used to harvest wind energy, only the disk-TENG 1220 can generate electric energy, and the function of the blades 1212 of the water-TENG 1210 is converting the wind energy to the mechanical rotation motion of the back disk 1224. In this case, there is no electrical output for the water-TENG 1210 as shown in FIG. 23, because the flowing water with tribo-charges is a necessary condition to generate electrical output for the water-TENG 1210.

3.3 Water-TENG and Contact-TENG 3.3.1 Structure

FIG. 24 illustrates a generator 2400 for harvesting energy from flowing water according to one aspect of the disclosed technology. The generator 2400 may include a water-TENG 2410 to collect the electrostatic energy of water and a contact-TENG 2420 to collect the mechanical/kinetic energy of water. Both the water-TENG 2410 and the contact-TENG 2420 may operate in a single-electrode mode.

Output 1 of the generator 2400 may include power generated from both the water-TENG 2410 and the contact-TENG 2420, whereas Output 2 of the generator 2400 may only include power generated from the contact-TENG 2420. Therefore, the power generated by the water-TENG 2410 is the difference between Output 1 and Output 2.

3.3.1.1 Water-TENG

The water-TENG 2410 may include a surface layer 2412. The surface layer 2412 may be superhydrophobic to enhance the electrostatic induction effect. In one example, the surface layer 2412 may include a TiO₂ layer 2414 with hierarchical micro-/nanostructures 2416 thereon.

The water-TENG 2410 may include an electrode 2418. The electrode 2418 may include, but not limited to, anyone or a combination of the following materials: metal such as copper, gold, silver and aluminum, indium tin oxide (ITO) and conductive polymer, among many other possibilities.

The surface layer 2412 may receive flowing water carrying triboelectric charges. The flowing water may affect a flow of electrons between the electrode and ground.

FIG. 25A displays a SEM image of assembled SiO₂ nanoparticles on the SiO₂ thin film. The inset of FIG. 25A shows that the nanoparticles are uniformly distributed on the surface. By contrast, FIG. 25B illustrates a prepared TiO₂ layer on a PET film with irregular structures. As illustrated in the inset of FIG. 25B, the irregular structures may be dendrite-like particles made of nanoplatelets. In one embodiment, the particles may have an average size of 180 nm and composed by nanoplatelets with an average width of 5 nm and length of 70 nm, respectively.

FIG. 26A illustrates the crystal phase of TiO₂ layer as identified by Raman spectroscopy. The Raman bands appearing at 137, 254, 430, and 605 cm⁻¹ can be assigned to the B_(1g), two-phonon scattering, E_(g), and A_(1g) modes of rutile phase, indicating that the dendrite-like particles are formed by rutile TiO₂ nanoplatelets. FIG. 26B illustrates the crystal phase of TiO₂ layer as identified by X-ray diffraction (XRD). The XRD pattern shows the characteristic diffraction peaks of rutile phase, which also validates the Raman spectroscopy result.

The TiO₂ layer with hierarchical micro-/nanostructures increases hydrophobicity of the water-TENG 2410. The ydrophobicity of the TiO₂ layer is assessed by measuring the contact angle of water drops. FIG. 27A illustrates that the measured contact angle of the TiO₂ layer is about 130°. Compared to the rutile form of smooth TiO₂ surface with a contact angle less than 80°, the increased contact angle in the TiO₂ layer is attributed to the hierarchical micro-/nanostructures that trap air, which, in turn, reduce the actual contact area between the surface and water drops. After a monolayer coating of 1H,1H,2H,2H-perfluorooctyltrichlorosilane (PFTS) on the TiO₂ layer, the measured contact angle of TiO₂ layer may be enhanced to 156° as illustrated in FIG. 27B, which may be referred to as superhydrophobic.

TiO₂ is selected due to its low cost, high chemical stability, excellent photocatalytic activity, and broad-spectrum antibacterial property. The use of TiO₂ nanomaterials in the water-TENG 2410 may not only harvest the electrostatic energy of water, but also provide the advantages of photocatalytic activity and antibacterial property for water purification.

3.3.1.1.1 Photocatalytic Activity of TiO₂

In one experiment, the photocatalytic activity of the TiO₂ layer 2414 is evaluated by the photodegradation of methylene blue (MB) under the solar light irradiation (intensity 100 mW cm⁻²), as illustrated in FIG. 28. The inset of FIG. 28 provides a comparison of photocatalytic activity without and with the prepared TiO₂ layer 2414.

In a typical experiment, the TiO₂ layer on PET film is dipped into a MB solution (10 mL, 20 μM). Prior to the irradiation, the solution is kept in the dark for 20 min to achieve the adsorption-desorption equilibrium between the TiO₂ nanomaterials and MB. Then, at certain time interval (every 15 min) during the irradiation process, the solution is analyzed with a UV-Vis spectrophotometer to measure the concentration change of MB. After the light irradiation for 90 min, almost all MB is photodegradated as compared to the control experiment in the absence of TiO₂ layer.

In the experiment, a 450-W xenon arc lamp (Oriel, Stratford, Conn.) equipped with an AM 1.5 filter is used as a solar irradiation source. A commercially available silicon-based reference cell is employed to examine the light intensity (100 mW cm⁻²).

3.3.1.1.2 Antibacterial Property of TiO₂

The antibacterial property of the TiO₂ layer 2414 against E. coli is also assessed. In one experiment, E. coli (DH5α) is grown in sterile LB medium. The medium is prepared by dissolving bacto-tryptone, bacto-yeast extract, and NaCl in deionized water. The solution is adjusted to pH 7.0 by adding NaOH. The E. coli is controlled to grow until the absorbance of the solution at wavelength 600 nm reached 1.0. A portion of the solution is centrifuged and washed with 0.85% NaCl to remove the matrix. Cells diluted to 4.0×10⁶ CFU mL⁻¹ are incubated in LB medium with and without the prepared TiO₂ layer under the solar light irradiation (intensity 100 mW cm⁻²). The viability assay is calculated by using SYTO 9 and propidium iodide (PI) dyes. The E. coli treated with the prepared TiO₂ layer is subject to three centrifugation/wash cycles and washed with 0.85% NaCl to remove the matrix. Then the suspension is mixed with the dyes. The mixtures are incubated for 15 min at 25° C. Fluorescence intensities of SYTO 9 (excitation wavelength of 475 nm, emission wavelength of 530 nm, green) and PI (excitation wavelength of 475 nm, emission wavelength of 640 nm, red) are recorded. The fluorescence intensity ratio of 530 nm/640 nm is used to calculate the percentage of live/dead cell population.

FIGS. 30A-B provide representative microscopic images of E. coli in LB media incubating without and with the TiO₂ layer under the light irradiation for 30 min. Fluorescent stains in FIG. 30A represent live cells, whereas fluorescent stains in FIG. 30B represent dead cells. The viability values of E. coli in the presence of the TiO₂ layer without and with the light irradiation are 84% and 17%, respectively.

3.3.1.2 Contact-TENG

The contact-TENG 2420 may be coupled to the water-TENG 2410. The contact-TENG 2420 may include a negative triboelectric charging material 2422 and a positive triboelectric charging material 2424. In one example, the negative triboelectric charging material 2422 may include but not limited to a PTFE layer. The positive triboelectric charging material 2424 may include but not limited to a layer of SiO₂ nanoparticles. SiO₂ nanoparticles 2424 may provide the advantage of larger contact surface area and enhance the electric output of the contact-TENG 2420.

When the water-TENG 2410 receives the flowing water, the water-TENG 2410 may contact the contact-TENG 2420 to affect a flow of electrons at the water-TENG 22410 and the contact-TENG 2420.

3.3.2 Fabrication

FIG. 29 illustrates an exemplary fabrication process of the generator 2400.

3.3.2.1 Fabricate Water-TENG

The water-TENG 2410 may use a polyethylene terephthalate (PET) film 2417. The PET film 2417 may have a thickness of 0.1mm.

Before the growth of TiO₂ layer with hierarchical micro-/nanostructures, the PET film may be ultrasonically cleaned in ethanol and water for 30 min, respectively. Then, the PET film may be placed in a glass bottle filled with TiCl₃ solutions (0.1 M). After 10 min, the glass bottle may be heated in an oven at 80° C. for 6 h and cooled in air. The growth cycle need to repeat 2 times to make sure the PET film surface is coated with a uniform TiO₂ layer.

During the growth of TiO₂ crystal, Ti(III) species may be gradually oxidized to Ti(IV) species by the dissolved O₂ and then hydrolyzed to form TiO₂. By increasing the reaction time and growth cycle, a TiO₂ layer 2414 with hierarchical micro-/nanostructures 2416 instead of vertically aligned TiO₂ nanoplatelet arrays is formed.

The TiO₂ layer 2414 coated PET film may be rinsed with water to remove the non-adsorbed TiO₂ nanomaterials and dried at ambient temperature. After that, the TiO₂ layer 2414 may be further coated with 1H,1H,2H,2H-perfluorooctyltrichlorosilane (PFTS) to increase the hydrophobicity. Specifically, the TiO₂ layer coated PET film may be immersed in 0.5% 1H,1H,2H,2H-perfluorooctyltrichlorosilane (PFTS) in hexane for 10 min, and washed with hexane to remove residual PFTS. After further drying at ambient temperature, the TiO₂ layer coated PET film may be treated in a vacuum oven at 110° C. for 1 h.

A Cu thin film 2418 (e.g., 100 nm) may be firstly deposited on the other side of the PET film 2417 as the electrodes for the water-TENG 2410. The Cu thin film 2418 may be connected with Output 1 of the generator 2400, including power generated from both the water-TENG 2410 and the contact-TENG 2420.

A commercial polytetrafluoroethylene (PTFE) film 2419 (e.g., 25 μm) may cover the top of the deposited Cu thin film 2418. On the other side of PET film, a TiO₂ layer 2414 with hierarchical micro-/nanostructures 2416 may grow directly through a facile, scalable, and low cost chemical bath method.

3.3.2.2 Fabricate Contact-TENG

The contact-TENG 2420 may use a poly(methyl methacrylate) (PMMA) sheet 2425. A Cu thin film 2426 may be deposited on one side of the PMMA sheet 2425 as the electrodes for the contact-TENG 2420. The Cu thin film 2426 may have a thickness of approximately 100 nm. The Cu thin film 2426 is the Output 2 of the generator 2400, which may only include the power generated from the contact-TENG 2420.

For purposes of generating triboelectric charges with a high density on the surface, silica (SiO₂) may be selected because it is positioned extremely positive in the triboelectric series. A SiO₂ thin film 2422 (e.g., 20 nm) may be deposited on top of the Cu thin film 2426. Then, a layer of SiO₂ nanoparticles 2424 may be assembled on the deposited SiO₂ thin film 2422 to increase the contact area. SiO₂ nanoparticles 2424 with an average size of 250 nm may be synthesized according to the Stober method. Typically, concentrated ammonia (28%, 3 mL) is added rapidly to the solution containing absolute ethanol (99.9%, 50 mL) and tetraethyl orthosilicate (99%, 1.5 mL). The mixture is reacted at ambient temperature for 24 h.

3.3.2.3 Assembly

A spacer 2430 may combine all parts of the generator 2400. For example, the spacer 2430 may be applied to maintain a gap distance between the PTFE film 2419 of the water-TENG 2410 and the SiO₂ nanoparticles 2424 of the contact-TENG 2420. The spacer 2430 may include a PET film. The spacer 2430 may have a thickness of about 0.5 mm.

3.3.3 Operating Principle

Both the water-TENG 2410 and the contact-TENG 2420 may operate in a single-electrode mode. FIG. 31A illustrates the working mechanism of the water-TENG 2410 of the generator 2400. When a water drop 3102 carrying positive charges contacts the TiO₂ layer 2414 as shown in step (ii), a positive electric potential difference may occur between the charged water drop 3102 and ground. This may cause the electrons to flow from ground to the electrode 2418 and generate an instantaneously opposite potential to balance the electric field, finally reaching equilibrium at step (iii). Once the charged water drop 3102 leaves the TiO₂ layer 2414, a negative electric potential difference may occur, forcing the electrons to flow from the electrode 2418 to ground at step (iv), until achieving another equilibrium at step (i).

FIG. 31B illustrates the working mechanism of the contact-TENG 2420 of the generator 2400. The impact force from the water drop may also drive the contact-TENG 2420 to work. The impact force from the water drop can overcome the resistance from the spacer 2430 to make the PTFE film 2419 of the water TENG 2410 contact the SiO2 nanoparticles 2424 at step (vi), causing the electrons to transfer from the SiO₂ nanoparticles 2424 to the PTFE film surface 2419 and leaving the SiO₂ nanoparticles 2424 a positively charged surface. As the water drop leaves the TiO₂ layer 2414, the contacted surfaces are separated, then a positive electric potential difference between the SiO₂ nanoparticles 2424 and ground and a negative electric potential difference between ground and the PTFE film 2419 are established at step (vii). This causes the electrons flowing from ground to the electrode 2424 and from the electrode 2418 to ground, finally reaching equilibrium at step (viii). This contributes to instantaneously positive and negative currents from the Output 2 and Output 1 of the generator 2400. Once another charged water drop falls on the generator 2400, and makes the PTFE film 2419 contact the SiO₂ nanoparticles 2424 again, a negative electric potential difference between the SiO₂ nanoparticles and ground and a positive electric potential difference between ground and the PTFE film 2419 may occur. This causes the electrons to flow from the electrode 2424 to ground and from ground to the electrode 2418 at step (ix), until achieving equilibrium at step (vi). This process corresponds to instantaneously negative and positive currents from the Output 2 and Output 1 of the generator 2400. So from the working mechanism of the generator 2400, when a charged water drop falls on the generator 2400, the generated outputs of the water-TENG 2410 and the contact-TENG 2420 may be simultaneous and in the same direction. If the charged water drop or flowing water contact and leave the generator 2400 periodically, both the outputs of the water-TENG 2410 and the contact-TENG 2420 may be continuously generated.

3.3.4 Output Performance

The measured signal of the Output 1 of the generator 2400 may contain the power generated from both the water-TENG 2410 and the contact-TENG 2420, while the measured signal of the Output 2 of the generator 2400 represents the power from the contact-TENG 2420.

In one experiment, the performance of the generator 2400 may be tested by using the flowing water from a household faucet. The flowing rate of water is controlled at 20 mL s⁻¹ and the distance between the generator 2400 and the outlet of faucet is 25 cm. The impact angle is optimized at 30°. The effective dimensions of the generator 2400 are 1.2 cm×1.2 cm. The open-circuit voltage (V_(oc)) and I_(sc) are measured to evaluate the performance of the generator 2400. FIGS. 32A-B illustrate typical V_(oc) and I_(sc) curves generated from the Output 1 and Output 2 of the generator 2400. FIG. 32A illustrates that the V_(oc) values of the Output 1 achieve 52 V. FIG. 32B illustrates that the V_(oc) values of the Output 2 achieve 35 V. FIG. 32C illustrates that the I_(sc) values of the Output 1 exceed 14 μA. FIG. 32D illustrates that the I_(sc) values of the Output 2 exceed 6.7 μA.

To investigate the output power density of the generator 2400, the generated V_(oc) and I_(sc) from the Output 1 and Output 2 of the generator 2400 when connected to an external load resistor are also measured. The resistance varies from 0.01 MΩ to 1 GΩ. As illustrated in FIGS. 33A-B, when the resistance is below 0.1 MΩ, the generated V_(oc) from the Output 1 (as illustrated in FIG. 33A) and Output 2 (as illustrated in FIG. 33B) of the generator 2400 is close to 0. Similarly, as illustrated in FIGS. 33C-D, when the resistance is below 0.1 MΩ, the generated I_(sc) from the Output 1 (as illustrated in FIG. 33C) and Output 2 (as illustrated in FIG. 33D) of the generator 2400 has only little changes. However, when the resistance is raised from 0.1 MΩ to 1 GΩ, the generated I_(sc) from the Output 1 and Output 2 of the generator 2400 through the load generally increases, but the generated I_(sc) from the Output 1 and Output 2 of the generator 2400 across the load decreases. As a result, the instantaneous power density generated from the Output 1 of the generator 2400 as illustrated in FIG. 33E and the instantaneous power density generated from the Output 2 of the generator 2400 as illustrated in FIG. 33F remain small with the resistance below 0.1 MΩ and achieve the maximum values of 1.31 W m⁻² and 0.38 W m⁻² at a resistance of 44 MΩ, respectively.

For the measurement of electrical outputs of the generator 2400, a programmable electrometer (Keithley Model 6514) and a low-noise current preamplifier (Stanford Research System Model SR570) are used.

3.3.5 Application 3.3.5.1 LED

In one experiment, to address the potential applications of the generator 2400, the generator 2400 is configured to have an increased effective dimension of 3.3 cm×3.3 cm as illustrated in FIG. 34. The flowing rate of water is raised to 40 mL s⁻¹. The distance between the generator 2400 and the outlet of faucet is 25 cm. FIG. 35A illustrates that the generated I_(sc) from the Output 1 of the generator 2400 may reach 43 μA. FIG. 35B illustrates that the generated I_(sc) from the Output 2 of the generator 2400 may reach 18 μA.

FIG. 36 illustrates the generated I_(sc) from a single water-TENG. As shown in FIG. 36, the value of the generated I_(sc) is 30 μA, which is smaller than the Output 1 of the generator 2400. By integrating the I_(sc) peak, collected charges from the Output 1 and Output 2 of the generator 2400 in a unit time may be determined as 3.3 μQ s⁻¹ and 1.4 μQ s⁻¹, respectively. A full-wave rectifying bridge may be applied to further transform the AC outputs to pulse outputs in the same direction. The rectified outputs from the Output 1 and Output 2 of the generator 2400 may drive commercial LEDs as illustrated in FIG. 37A and charge 33-μF capacitors as illustrated in FIG. 37B. The effective dimensions of the generator may be 3.3 cm×3.3 cm.

3.3.5.2 Self-Powered Nanosensor for Ethanol Detection

The water-TENG may be used as a self-powered nanosensor for ethanol detection. In one experiment to realize the concept, a programmable syringe pump (PHD 2000, Harvard Apparatus) is applied to control the volume each sample drop (30 μL). The sample drop is set up to fall from a height of 50 cm. FIG. 38A displays the output I_(sc) of the water-TENG generated by deionized water drops. As illustrated in FIG. 38A, the output I_(sc) reaches a value of 14 μA. The inset of FIG. 38A shows that the generated output is capable of turning on a commercial LED as indicator.

However, as shown in FIG. 38B, when the sample is changed from deionized water to a solution containing 20% ethanol (percentage by volume), the generated I_(sc) of the water-TENG is decreased to 3 μA. FIG. 38C illustrates the relationship between the generated I_(sc) and ethanol concentration. By connecting the water-TENG with a LED (indicator), a stand-alone and self-powered ethanol nanosensor may be formed. The inset of FIG. 38B reveals that the LED powers off when detecting the 20% ethanol solution. In other words, the generated output in FIG. 38B cannot drive the LED.

The decrease in the generated I_(sc) may be caused by the reduced charges on the sample drop. By integrating the I_(sc) peak of water-TENG generated at different ethanol concentration, the inductively transferred charges on the Cu electrode may be deduced, which may be proportional to the triboelectric charges on sample drop. FIG. 38D illustrates that the triboelectric charges on a sample drop decrease when raising ethanol concentration.

Ethanol is capable of removing the triboelectric charges. Hence, the presence of ethanol may reduce the triboelectric charges on sample drop surface and decrease the electrical output of water-TENG. Compared to another self-powered ethanol sensor based on the contact electrification of hydrophobic polymer film and sample, the as-developed water-TENG is not only a new design but also has the advantage of minimizing the sample volume.

The combination of a commercial LED with water-TENG indicates that the sensing system toward ethanol detection may be simplified by replacing the electrometer with an LED.

In one embodiment, the generator 2400 as shown in FIG. 24 may be coupled to a power indicator. The surface layer 2412 may receive a solution containing a chemical and water, where the chemical may remove at least one triboelectric charge from the water. The power indicator may indicate whether the chemical is present based on power output of the triboelectric generator. In one example, the chemical is ethanol. The power indicator may be an LED.

4. Summary

The disclosed technology provides a green and sustainable solution for harvesting multiple types of energies from the environment, including but not limited to, energies from water flow such as tap water flowing from a household faucet, raindrop, ocean wave and wind. Types of water which the energies may be harvested from include deionized, tap and salt water, among many other possibilities.

The disclosed technology may have many applications, including, but not limited to, powering low power applications including but not limited to light emitting diodes, sensors and portable electronics, and charging capacitors. The disclosed technology may be adapted to many applications, including but not limited to, self-powered sensors for detecting flowing water rate, wind speed, chemicals such as ethanol, temperature, and water/liquid leakage from a container/pipe.

Numerous characteristics and advantages have been set forth in the foregoing description, together with details of structure and function. While the invention has been disclosed in several forms, it will be apparent to those skilled in the art that many modifications, additions, and deletions, especially in matters of shape, size, and arrangement of parts, can be made therein without departing from the spirit and scope of the invention and its equivalents as set forth in the following claims. Therefore, other modifications or embodiments as may be suggested by the teachings herein are particularly reserved as they fall within the breadth and scope of the claims here appended. The term “exemplary” used herein does not mean best mode, but rather, example.

Accordingly, those skilled in the art will appreciate that the conception upon which the application and claims are based may be readily utilized as a basis for the design of other structures, methods, and systems for carrying out the several purposes of the embodiments and claims disclosed in this application. It is important, therefore, that the claims be regarded as including such equivalent constructions.

Furthermore, the purpose of the foregoing Abstract is to enable the public generally, and especially including the practitioners in the art who are not familiar with patent and legal terms or phraseology, to determine quickly from a cursory inspection the nature and essence of the technical disclosure of the application. The Abstract is neither intended to define the claims of the application, nor is it intended to be limiting to the scope of the claims in any way. 

The invention claimed is:
 1. A generator comprising: blades arranged in a radially outward fashion, each blade including: an electrode; and a surface layer for receiving flowing water carrying triboelectric charges, the flowing water affecting a flow of electrons between the electrode and ground.
 2. The generator of claim 1, wherein the blades exhibit a wheel-like structure.
 3. The generator of claim 1, wherein the surface layer is superhydrophobic.
 4. The generator of claim 1, wherein the surface layer includes nanosturctures thereon.
 5. The generator of claim 1, wherein the surface layer includes at least one material selected from the group consisting of polyethylene terephthalate, poly(methyl methacrylate), polydimethylsiloxan, polytetrafluoroethylene, fluorinated ethylene propylene, poly(vinyl chloride), polyimide, metal and alloy.
 6. The generator of claim 1, wherein the electrode includes at least one material selected from the group consisting of metal, indium tin oxide and conductive polymer.
 7. The generator of claim 1 further comprising and a a rotatable disk that rotates when the blades receive the flow water; wherein the rotatable disk harvests mechanical kinetic energy from the flowing water during rotation.
 8. The generator of claim 7, wherein the rotatable disk comprises two segmented disks; and wherein each segmented disk includes an electrode.
 9. A generator comprising: an electrode; and a superhydrophobic surface layer for receiving an energy flow carrying triboelectric charges, the surface layer including a TiO₂ layer with nanostructures thereon, the energy flow affecting a flow of electrons.
 10. The generator of claim 9, wherein the energy flow is water flow; and wherein the water flow affects a flow of electrons between the electrode and ground. 